1. Field of the Invention
The present invention relates to a humidifier for properly humidifying a gas to be supplied to a patient for narcotization in surgical operation, for artificial respiration to cure the patient of difficulty of breathing or for oxygen inhalation.
2. Description of the Prior Art
Referring to FIG. 1 showing a conventional humidifier for such a purpose, a medical gas supplied by a respirator or an anaesthesia apparatus flows into a humidifying chamber 16' through the inlet 31 thereof as indicated by an arrow A, the medical gas heated and humidified in the humidifying chamber 16' flows out of the humidifying chamber 16' through an outlet 32 as indicated by an arrow B, and the heated and humidified medical gas is supplied to the patient through a patient circuit 17' having one end connected to the outlet 32 of the humidifying chamber 16' and the other end connected to the patient as indicated by an arrow 33. An air way temperature sensor 12' provided at the outlet of the patient circuit 17' detects the temperature of the medical gas. A heater 9' for heating the humidifying chamber 16' is controlled on the basis of the detection signal provided by the air way temperature sensor 12'.
Although the medical gas is heated and humidified properly in the humidifier, more specifically, by the humidifying chamber 16', dew drop occurs on the inner surface of the patient circuit 17'because, in most cases, the room temperature is lower than the temperature of the patient circuit 17', In the worst case, it is possible that water condensed in the patient circuit 17' flows into the trachea of the patient, risking the patient. Furthermore, some papers report that the degree of bacterial contamination of the interior of the pipe increases with the moisture in the pipe.
FIG. 2 shows another conventional humidifier incorporating improvements for eliminating the disadvantages of the humidifier shown in FIG. 1. This humidifier has a patient circuit 17' connecting a humidifying chamber 16' to a patient and internally provided with a heated wire 10' connected in parallel to a heater for 9' for heating the humidifying chamber 16'. The heated wire 10' heats the interior of the patient circuit 17' to prevent said dew drop within the patient circuit 17'. However, when the difference between the setting temperature and the room temperature is small, the medical gas is heated to the set temperature only by the heated wire 10'. In such case that the temperature of the humidifying water contained in the humidifying chamber 16' is low and the medical gas is heated to the set temperature by the heated wire 10', the relative humidity of the medical gas is reduced below an undesirable level.
As shown in FIG. 1 or FIG. 2, a temperature signal obtained by the temperature sensor 12' is displayed via the amplifier 25 and the digital display circuit 27.
Also both an output of the amplifier 25 and a signal from a temperature setting switch 29 are inputted to a temperature proportional control circuit 28.
An output signal of a circuit 28 can control the temperature of the heater 9' through an SSR 7'.
Further 18' and 19' are constructed as an electric source.
FIG. 3 shows a third conventional humidifier incorporating improvements to solve the foregoing problems. This humidifier is provided with a humidifying chamber temperature sensor 11' for detecting the temperature of the medical gas at the outlet of a humidifying chamber 16". The output signal of the outlet temperature sensor for humidifying chamber 11' is applied through an amplifier 24 to a temperature proportional control circuit 28' for feedback control. A heater for humidifying chamber 9'for heating the humidifying chamber 16' is controlled so that the outlet temperature for the humidifying chamber, namely, the temperature of the gas at the outlet of the humidifying chamber 16', is in the range of a set temperature set by a temperature setting switch 29 plus 2.degree. C. to plus 3.degree. C. to compensate beforehand the moisture corresponding to the condensate that may be formed within a patient circuit 17". In addition, a heated wire 10" is controlled so that a temperature represented by the output signal of an air way temperature sensor 12' coincides with the set temperature.
In FIG. 3, an amplifier 23 corresponding to the amplifier 25 as shown in FIG. 1 or FIG. 2, and another amplifier 24 amplifying the signal obtained by a sensor 11' are inputted respectively to a digital display circuit 27 and a temperature proportional control circuit 28.
Further an SSR 7" and a SSR 8" are separated in function as shown in FIG. 1 and FIG. 2 respectively, and 10" is shown as a heater.
However, condensation in the patient circuit 17" is unavoidable because a gas of a saturated humidity flows through the patient circuit 17", and the gas is cooled due to the difference between the temperature of the gas and the room temperature which is normally cooler than said gas. Although the quantity of condensate formed in the patient circuit 17" of the third conventional humidifier is somewhat smaller than that of condensate formed in the patient circuit 17' of the first or second conventional humidifier, the performance of the third conventional humidifier is not satisfactory.